1. Field of the Invention
The present invention relates to a magneto-optical recording medium in which information can be overwritten by the magnetic field modulation method.
2. Description of Related Art
Various proposals have been made to overwrite information onto a magneto-optical recording medium (hereinafter referred to as a recording medium) by the magnetic field modulation method. In overwriting information by the magnetic field modulation method, a laser beam of constant light intensity is projected onto the recording medium and a modulated magnetic field of a predetermined intensity is applied to the position of the recording medium onto which light is projected, whereby the information already recorded in the recording medium is erased and at. the same time fresh information is stored therein. The result of a research of the magneto-optical recording by the magnetic field modulation method mentioned above has been disclosed, for example, in "Magnetics Research MAG-87-173-180", published by a corporate juridical person: Japanese Electrotechnical Committee in Nov. 24, 1987.
Meanwhile, in or der to write information into the recording medium with high density, it is necessary to raise the modulation frequency of a magnetic head applying the modulated magnetic field. Besides, it is also required to increase the distance between the magnetic head and the recording medium in view of irregularity in thickness and warping of the recording medium.
If the modulation frequency is raised, however, the intensity of the magnetic field generated by the magnetic head is reduced. Moreover, because of the high speed rotation of the recording medium, the intensity of the modulated magnetic field applied to the recording medium is unable to keep up with the modulated magnetic field of the magnetic head, which results in the deterioration of the intensity of the modulated magnetic field applied to the recording medium. The intensity of the modulated magnetic field applied to the recording medium is further deteriorated also due to the increased distance between the magnetic head and the recording medium.
Accordingly, it is required to make the intensity of the modulated magnetic field of the magnetic head not less than 200 Oe for the purpose of recording information in the recording medium in a sufficient recording state. The reason for this is considered to reside in the fact that the floating magnetic field generated by the recording medium itself opposes or repels the modulated magnetic field applied from the magnetic head.
Wherever in this specification reference is made to various media parameters, such as magnetization M.sub.s and coercive H.sub.C, it will be understood by those skilled in the art that the values are those determined at room temperature, unless otherwise indicated.